Open vSwitch GRE-over-IPsec support

Open vSwitch is a production quality, multilayer, software-based, Ethernet
virtual switch. It is designed to enable massive network automation through
programmatic extension, while still supporting standard management interfaces
and protocols (e.g. NetFlow, sFlow, SPAN, RSPAN, CLI, LACP, 802.1ag). In
addition, it is designed to support distribution across multiple physical
servers similar to VMware's vNetwork distributed vswitch or Cisco's Nexus
1000V.

The ovs-monitor-ipsec script provides support for encrypting GRE
tunnels with IPsec.